1. Field of the Invention
The present invention generally relates to a brake control apparatus that achieves a deceleration corresponding to the amount by which a driver operates the brake. More specifically, the present invention relates to a brake control apparatus in a vehicle equipped with a regenerative braking device (e.g., a motor generator) and a hydraulic braking device (e.g., wheel cylinders).
2. Background Information
Some hybrid vehicles and electric vehicles are equipped with a hydraulic braking system and a motor-generator that also functions as a regenerative braking system. The regenerative braking system uses the motor-generator as a generator when a driver releases his foot from an accelerator pedal or when a brake pedal is depressed, and to decelerate a vehicle by transforming kinetic energy into electrical energy (regenerative braking). The electrical power which is then generated is stored in a battery or capacitor. An example of a brake control apparatus for controlling vehicles equipped with a hydraulic braking system and a regenerative braking system is described in Japanese Laid-Open Patent Publication No. 7-223532. This brake control apparatus calculates a braking force command value based on the deceleration corresponding to the amount by which the driver operated the brake, apportions the result into a braking force command value for the regenerative braking system and a braking force command value for the hydraulic braking system. The brake control apparatus then controls the braking forces applied to the wheels based on these command values.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved brake control apparatus that suppresses fluctuations in the deceleration when changing from cooperative braking to only regenerative braking or only hydraulic braking. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that in the aforementioned brake control apparatus, the regenerative braking force varies depending upon the traveling speed of the vehicle, and it is necessary to change the braking force apportioned to the hydraulic braking system in response to the change in the regenerative braking force. It has also been discovered that regenerative braking systems have different control precision and response times in comparison to hydraulic braking systems. These differences between the two braking systems cause the deceleration experienced by the vehicle or the wheels to fluctuate.
The present invention was developed in order to solve these problems. One object of the present invention is to provide a brake control apparatus that can stabilize the deceleration experienced by the wheels.
In order to achieve the aforementioned object, a brake control apparatus is provided that basically comprises a hydraulic braking system, a regenerative braking system, a target deceleration setting device, a deceleration detecting device, a braking force command value calculating device, a braking force apportioning device, a phase compensating device, a hydraulic braking control device and a regenerative braking control device. The hydraulic braking system is configured to impart a hydraulic braking force to a wheel using brake fluid pressure with a hydraulic braking response characteristic. The regenerative braking system is configured to impart a regenerative braking force to the wheel using regenerative braking with a regenerative braking response characteristic. The target deceleration setting device is configured to set a target deceleration based on a signal indicative of a braking operation amount. The deceleration detecting device is configured to detect a deceleration experienced by the wheel. The braking force command value calculating device is configured to calculate a braking force command value that is needed to cause the deceleration detected by the deceleration detecting device to substantially match the target deceleration set by the target deceleration setting device based on an ideal reference model response characteristic. The braking force apportioning device is configured to apportion the braking force command value calculated by the braking force command value calculating device into a hydraulic braking force command value to be applied by the hydraulic braking system and a regenerative braking force command value to be applied by the regenerative braking system. The phase compensating device is configured to apply a phase compensation to at least one of the hydraulic braking force command value and the regenerative braking force command value obtained by the braking force apportioning device such that the hydraulic braking response characteristic of the hydraulic braking force command value and the regenerative braking response characteristic of the regenerative braking force command value substantially match a vehicle model response characteristic. The hydraulic braking control device is configured to control the hydraulic braking force applied to the wheel by the hydraulic braking system based on the hydraulic braking force command value that has been phase compensated by the phase compensating device. The regenerative braking control device is configured to control the regenerative braking force applied to the wheel by the regenerative braking system based on a regenerative braking force command value that has been phase compensated by the phase compensating device.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.